For a liquid crystal display element to function, the direction of orientation of liquid crystal molecules between two substrates and the direction of polarization of polarizers laminated to the substrates must be set in a particular relation to each other. In liquid-crystal display element technologies, LCDs using a TN (Twisted Nematic) type liquid crystal were the first to be put into practical use. Recently, LCDs using a VA (vertical Alignment) type liquid crystal, an IPS (Inplane Switching) type liquid crystal etc. were put into practical use. Although a technical explanation is omitted, in an LCD using such TN-type liquid-crystal panel, liquid crystal molecules are provided between two upper and lower orientation films having respective rubbing directions on the inner surfaces of substrates of the liquid-crystal panel. This means that the liquid crystal molecules are twisted by 90 degrees along the optical axis, so that, when a voltage is applied, the liquid crystal molecules are aligned in a direction perpendicular to the orientation films. However, in case where the LCD is designed to allow images of the same quality to be seen as viewed from right and left sides of a display screen as those view from directly in front of the display screen, the direction of rubbing on the orientation film at the viewing-side must be 45 degrees (the rubbing direction of the other orientation film being 135 degrees). It is therefore necessary that the polarizing sheets made from the polarizing composite films as shown in FIGS. 1A and 1B, for laminating respectively on the front and back sides of the liquid-crystal panel with adhesive layers must have polarizers respectively oriented in directions inclined respectively by 45 degree with respect to a lengthwise or widthwise direction of the display screen so as to conform to the rubbing directions.
Therefore, in an optical film for use in producing a liquid-crystal element of a TN-type liquid-crystal panel, it is required that the optical film is punched or cut into a rectangular-shaped sheet having a major side or a minor side determined in accordance with the size of the TN liquid crystal panel and inclined by 45 degrees with respect to the orientation direction of the polarizer, as described in Japanese Laid-Open Patent Publication No. JP 2003-161935A or Japanese Patent 3616866B.
The punching or cutting the optical film into the rectangular-shaped sheet may be collectively referred as “individualized sheet” or “method and system for manufacturing individualized sheet” for a liquid-crystal display element. The sheet of optical film thus punched or cut is produced by punching or cutting in the form including the protective carrier film so that any exposure of the adhesive layer in the polarizing composite film contained in the optical film can be prevented. The punched-out or cut sheet of the carrier film may be referred as “separator”, rather than “sheet of the carrier film”. Thus, the manufacturing process of the liquid-crystal display elements includes the first step of peeling the separator from each of the sheets of optical film to have the adhesive layer exposed. Subsequently, the sheets of the optical film each having the adhesive layer exposed by peeling the separator are conveyed one-by-one by for example under a vacuum suction irrespective of whether the surface protective films are laminated or not, and laminated to respective ones of a plurality of liquid-crystal panels. According to the aforementioned manufacturing process of the liquid-crystal display elements, it has been required that the punched-out or cut sheet is in the form of an individualized sheet having four trimmed sides and a certain level of stiffness. During the initial period in the history of the manufacturing process of the liquid-crystal display elements, this polarizing sheet having four trimmed sides was generally been known as a “polarizing plate” which is still used as a common name.
In the manufacturing process of TN-type liquid-crystal display elements, an optical film unwound from a roll of the optical film may be sequentially punched or cut in a direction transverse to the feed direction. However, in this case, it is impossible to obtain a finished liquid crystal display element simply by laminating the polarizing sheets formed to respective ones of a plurality of liquid-crystal panels. This is because the polarizing sheets each formed with a major or minor side extending in a direction 45 degrees cannot be laminated sequentially to respective ones of the liquid-crystal panels W with the same posture. Therefore, to provide a finished liquid crystal display element by feeding a polarizing sheet formed from a polarizing composite film included in a continuous web of polarizing composite film being fed, a polarizing composite film having a width greater than a major side of a liquid-crystal panel W is required. Further, polarizing composite film must be punched at an angled direction of 45 degrees with respect to the lengthwise direction into a plurality of individual polarizing sheet as seen in Japanese Laid-Open Patent Publication No. JP 2003-161935A or Japanese Patent 3616866 B. Alternatively, an elongated polarizing composite film may be provided in the form of a single sheet by punching or cutting it in a direction 45 degrees inclined with respect to the lengthwise direction, or by connecting a plurality of such sheets into a film-like configuration, and winding the film to form a roll of the polarizing composite film. The elongated polarizing composite film is then used in a process of forming polarizing sheets, by unwinding the polarizing composite film from the roll, and cutting into a required size each of the polarizing sheets and laminated to a respective one of a plurality of liquid-crystal panels W. Therefore, all of the above techniques require a system that manufactures individualized sheets.
Before VA-type liquid crystal and IPS-type liquid crystal were brought into practical use, Japanese Patent Publication No. 62-14810 B disclosed continuously feeding an optical film including a polarizing composite film. Japanese Patent Publication No. 62-14810 B discloses a technique of continuously feeding an optical film which comprises a polarizing composite film (called an “elongated polarizing plate”) and a separator for protecting an adhesive layer on the polarizing composite film onto a plurality of liquid-crystal panels (called “liquid-crystal cells”) for small-size display screens of electronic calculators or the like utilizing a carrier function of the separator, cutting only a polarizing plate and an adhesive layer while leaving a separator uncut (hereinafter referred as “half-cut”)”, removing defective sheets of polarizing sheets in the course of the feeding, sequentially laminating the remaining polarizing sheets to the liquid-crystal panels, and peeling the separator off the polarizing sheets. The apparatus may be a so-called “labeler unit”. However, this liquid-crystal panel is an LCD using a TN-type liquid crystal, so that the optical film herein used must be an elongated sheet cut in a direction 45 degrees oblique to the longitudinal direction of the optical film. This technique cannot be practically applied directly to an optical film continuous feed apparatus for use in continuous manufacturing of a large-size liquid-crystal display element for widescreen televisions because of the width of optical film required.
Automation of process for manufacturing liquid-crystal display elements using individualized sheets is generally described below. For example, in Japanese Laid-Open Patent Publication No. 2002-23151A, the manufacturing process utilizing such individualized sheets has problems not only in that the separators must be removed from respective ones of the individualized sheets taken out from the magazine, but also in that the individualized sheets are flexible and are easily curved or distorted while they are being carried under suction, so that difficulties have been encountered in maintaining accuracy and speed in automatic registration and automatic lamination with liquid-crystal panels. Thus, it will be understood that the individualized sheet is required to have a certain level of thickness and stiffness to facilitate transport under suction and handling for automatic laminating process. For example, Japanese Laid-Open Patent Publication No. 2004-144913A, Japanese Laid-Open Patent Publication No. 2005-298208A or Japanese Laid-Open Patent Publication No. 2006-58411A discloses measures for addressing such technical problems.
On the other hand, the VA-type and IPS-type liquid-crystal panels are not designed to arrange liquid crystal molecules in twisted orientations. Thus, in these types of liquid-crystal panels, there is no need to have the polarization axis of the polarizing sheet oriented 45 degrees, but only required to have the polarizing sheets applied to the opposite sides of the liquid crystal display panel oriented with their polarization axes crossed at 90 degrees crossing angle. Rather, in the case of the VA-type and IPS-type liquid-crystal panels, with respect to the viewing angle characteristics, maximum contrast can be obtained along the direction of the polarizing axis of the polarizing sheet, so that it is preferable that the polarizing sheets have polarization axes oriented in parallel with the longitudinal or transverse direction of the liquid crystal panel from the view point of symmetry of the viewing angle characteristics and visibility. Thus, the polarizing sheets that including a polarizing composite film which has been subjected to a longitudinal or transverse stretching can be continuously unwound from a roll and cut along transverse lines to sequentially produce rectangular polarizing sheets.
Because of the improved viewing angle characteristics, VA-type liquid crystal or IPS-type liquid crystal are becoming more widely adopted than TN type liquid crystal. In view of such trend in environments of technical developments, proposals have been made such as the one described in Japanese Laid-Open Patent Publication No. 2004-361741A that are based on use of the VA-type or IPS-type liquid-crystal panels and comprise steps of continuously feeding an optical film laminate, cutting an optical film laminate in conformity to the size of a liquid-crystal panel and sequentially laminating polarizing sheets to respective ones of a plurality of the liquid-crystal panels.
However, the mainstream of manufacture of liquid-crystal display elements is still based on manufacturing technology utilizing individualized sheets, due to the following technical problems. In manufacturing liquid crystal display elements, a critical technical challenge is to detect any defect which may otherwise be retained in the display elements to be formed, and to prevent any defective product from being produced. This makes it possible to significantly improve manufacturing yield. Most of the product defects primarily arise from defects inherent in the polarizing composite film contained in the optical film. However, it is not practical to provide an optical film after completely removing all defects contained in individual films which are to be laminated together to form the optical film. The reason is that, observation of the polarizer, protective film laminated on the polarizer and an adhesive layer formed on the films indicates that there are various kinds of defects distributed in 20 to 200 positions over a unit length of the polarizing composite film of 1000 m This means that, under existing circumstances, it is extremely difficult to produce a defect-free optical film. In a finished display, flaws or defects, even if such a flaw or defect is small, are not permitted. Therefore, if a length of the polarizing composite film with defects are used to form a display and a display requires 1 m of film, 20 to 200 defective displays are produced per 1,000 displays produced.
A proposed preliminary inspection apparatus for use in individualized sheets is disclosed, for example, in Japanese Patent No. 3974400B, Japanese Laid-Open Patent Publication Nos. 2005-62165A and 2007-64989A.
Japanese Laid-Open Patent Publication 2007-140046A discloses a manufacturing method wherein an optical film (called “polarizing plate stock”) is continuously unrolled from a roll of the optical film in the form of a laminated structure. A carrier film (called “releasable film”) is peeled from the laminate of the optical film before the polarizing composite film in the optical film is inspected for existence of defects, then after the inspection, the polarizing composite film is punched or cut avoiding positions of defects.
Japanese Patent Application No. 2007-266200 discloses a method and an apparatus for laminating an optical film onto a liquid-crystal panel. The method and an apparatus disclosed in Japanese Patent Application No. 2007-266200, however, require steps that cause substantial complexity in the entire system for laminating but also an increase in the number of steps and difficulty in control for each step, and therefore, cause corresponding reduction in the manufacturing speed.
The present disclosure has been made based on the above related disclosures and through intensive research and consideration for significantly enhancing product accuracy and manufacturing speed, and drastically improving production yield, in the manufacture of liquid-crystal display elements.